1. Field of the Invention
This invention relates to a low-melting modified polyester resin capable mainly of notably reducing ply separation of hot-melt-adhesive conjugate fibers, and hot-melt-adhesive composite fibers using the above resin. More particularly, the invention relates to a low-melting, modified polyester resin capable of affording conjugate fibers having a broad hot-melt-adhesive temperature range and also having a high breaking strength. This invention is particularly useful in the case where the polyester resin is used as a part of or in place of the components of conventional hot-melt-adhesive conjugate fibers which is subjected to hot-melt-adhesive used, for example in the fields of paper diaper, hygienic goods, etc.
2. Description of the Related Art
Processes for producing non-woven fabrics by utilizing hot-melt adhesion of a low-melting component of conjugate fibers consisting of a plurality of polymers having different melting points have already been known. Such processes are suitable mainly for producing non-woven fabrics having a medium or low basis weight.
Japanese patent publication No. Sho 55-17807 discloses polyolefin conjugate fibers whose fiber-forming component is polypropylene and the adhesive component of which is polyethylene. However, such fibers have a relatively small difference in the melting points of the two components so that the temperature range in which hot-melt adhesion can be carried out in a state of low percentage of heat shrinkage is so narrow that a precise temperature control is required for producing non-woven fabrics.
Further, Japanese patent application laid-open No. Sho 57-176217 discloses conjugate fibers whose fiber-forming component is a polyester and the adhesive component of which is polypropylene or polyethylene. Since the fibers have a large difference in the melting points of the two components, the fibers have an advantage that the range of the hot-melt adhesion temperature is far broader than that of the above polyolefin conjugate fibers, but on the other hand, the compatibility between the polyester and the polyolefin is inferior so that there is a drawback that the two components are liable to peel off from each other. Further, since the conjugate fibers are heat-treated in advance in order to prevent shrinkage at the time of hot-melt adhesion, there are drawbacks that the fibers are in a state of being more readily peeled off from each other. Thus non-woven fabrics produced from such conjugate fibers possess a low stiffness. Consequently after a load has been repeatedly applied onto the fibers, the resulting fibers exhibit inferior restoration properties and low frictional resistance. Also when the fibers are peeled off the polyethylene is separated into powder.
Further, Japanese patent publication No. Hei 1-20249 discloses conjugate fibers obtained by hot-melt-adhering a fiber-forming component consisting of a copolymer of a modified polyolefin containing carboxyl group with a polyamide and a polyester and an adhesive component consisting of a modified polyolefin containing carboxyl group and an unmodified polyolefin or the mixture of the two. In the case of such fibers, problems so far raised are considerably overcome, that is, ply separation is difficult to occur and further, the temperature range of hot-melt-adhesion becomes broader. However, quality improvement in conjugate fibers used for paper diaper, hygienic goods, etc. has now been more and more required. In particular, the breaking strength of non-woven fabrics is still insufficient so that more improvement therein has been desired.
Thus, the present inventors have made extensive research in order to overcome the above-mentioned drawbacks of hot-melt-adhesive conjugate fibers, and as a result have achieved the present invention.